This invention relates to an engine exhaust gas cleaning system and more particularly to an improved arrangement for introducing secondary air to an exhaust gas catalyzer.
In order to control the emission of unwanted exhaust gas constituents, a wide variety of devices have been proposed. Frequently, catalytic converters are employed for treating the exhaust gases before their discharge to the atmosphere. As is well known, a catalytic converter must be operated at the appropriate temperature in order for it to effectively treat the exhaust gases.
For this reason, it has been proposed to place the catalytic converter as close to the exhaust ports of the engine as possible. However, frequently a single catalytic converter is not sufficient to provide all of the desired exhaust gas treatment. Therefore, it has been proposed to employ plural catalytic converters in series along the exhaust system.
Where this is done, the downstream catalytic converter will receive exhaust gases that have been previously treated. A converter in effect causes afterburning of the exhaust gases and this is one way in which their unwanted exhaust gas constituents are controlled. However, the downstream catalytic converter will not receive exhaust gases that are adequate to permit afterburning.
It has, therefore, been proposed to add supplemental air to the exhaust system between the upstream and downstream converters so that the downstream converter can effectively treat the exhaust gases. One way in which this is done is to provide an atmospheric air inlet to the downstream catalytic converter which will introduce air to the converter so as to permit more effective afterburning. This has been done by providing a jacket around the catalytic converter with the upstream end of the jacket being in communication with the atmosphere and the downstream end being in communication with the converter. This type of system has been proposed for use with motorcycles.
There are a number of disadvantages of this type of system. First, since the supplemental air is drawn from the atmosphere, there is a risk that the exhaust gases may flow back into the atmosphere through the supplemental air passage inlet. This problem can be particularly acute where the application is with a motorcycle since the air inlet is in proximity to rider of the motorcycle. In addition, exhaust gas sounds to emanate can the atmosphere through the supplemental air inlet.
In addition to the aforenoted defects, the atmospheric air which is drawn into the system will be cold and this can detract from the efficiency of the converter. That is, the drawing of cold atmospheric air into the converter can lower its temperature and make the system inefficient.
It is, therefore, a principal object to this invention to provide an improved engine exhaust gas cleaning system.
It is a further object to this invention to provide an improved engine exhaust gas cleaning system that employs supplemental air for a catalytic converter but wherein the supplemental air is drawn in such a way that exhaust gas noises and exhaust gases cannot be discharged to the atmosphere at an undesirable location.
It is a further object to this invention to provide an arrangement for introducing supplemental air to a catalytic converter wherein the supplemental air is preheated.
It is a still further object to this invention to provide an improved silencing system for the supplemental air drawn for a catalytic converter.